[jsr342-experts] Re: managed bean alignment

From: Reza Rahman <reza_rahman_at_lycos.com>
Date: Wed, 11 Apr 2012 12:57:29 -0400

I'll try to provide detailed responses to your questions in the next few days. Thanks for the patience.

-----Original Message-----
From: Linda DeMichiel [mailto:linda.demichiel_at_oracle.com]
Sent: Friday, April 06, 2012 5:59 PM
To: jsr342-experts_at_javaee-spec.java.net; reza_rahman_at_lycos.com
Subject: [jsr342-experts] Re: managed bean alignment

Thanks for the input. This is a helpful start to the discussion.
More inline below....

On 4/5/2012 5:50 PM, reza_rahman_at_lycos.com wrote:
> Firstly, I am glad we are finally getting to this very critical issue. Secondly, thanks for doing such a thorough job analyzing this.
> This is an issue we've discussed extensively and repeatedly at Caucho and hence I can offer what I think is a fairly well thought out opinion. Unfortunately, it can't be as simple as picking one of the matrices. I hope you'll forgive me and try to find a way of reconciling what I have below:
> * Java EE Managed Beans:
> We found that the @ManagedBean annotation is actually a source of confusion/frustration for most developers. I think it's best to gradually prune this annotation or simply leave it be. The overall concept is very good though and definitely should be kept around. The way we look at it, the fundamental concept serves as the unifying component model whereas all the other Java EE APIs can add their own services, including CDI. The basic question then really becomes which Java EE services are "legal" to be used on the very same managed bean. You could think of this as a kind of "service compatibility" matrix, in a much similar vein to yours.

Right. This is what we want expert group input on! How should such services be expanded? Which of the current JavaEE/EJB services should be extended to CDI "managed beans"? What of the CDI functionalities should be made available to which Java EE managed objects? To move forward we need more feedback from the group on the specifics.

> * @Resource, @EJB:
> These two annotations are largely redundant with CDI. It's best to gradually prune these annotations or simply leave them be. We should try to find a way of merging whatever remaining functionality they have with CDI.

Could you expand further as to how you see @Resource being redundant?
@Resource also functions as a means to specify the binding of a logical resource to the actual resource in the environment. How would you see this happening in the absence of @Resource in CDI?

> * Java EE interceptors:
> These were a fairly hasty and poor attempt at addressing cross-cutting concerns. It's best to gradually prune this or simply leave them be and focus on CDI annotations. Alternatively, perhaps CDI annotations should be merged back with this (harder to do I think).

Our opinion has been that we should leverage the CDI interceptor capabilities more broadly, as we proposed with the use of transactional interceptors. Again, in the attempt to be more concrete, our matrices illustrate the possible extents to which the use of interceptors might be expanded. For example, as noted in my writeup, we would also like to explore leveraging CDI interceptors as a more general mechanism to provide "container-managed" security.
We've also been discussing with the Bean Validation and CDI specleads how CDI interceptors might be leveraged as a mechanism to provide method-level validation.

> * EJBs:
> There are few valid reasons left for EJB to continue to have it's own component model. It increases the learning curve for new developers and has always proven to be a sticking point for Java EE adoption. It's best to gradually prune this or simply leave them be. As you suggested, let's separate the very useful EJB services from the component model and make them usable in managed beans as much as possible, likely as CDI "system" interceptors.

Yes. This separation is what we are suggesting -- the migration of container-managed services that EJB currently provides to other component types via a more generalized alignment around the notions of managed beans and interception. If we are successful in this, then yes, we will eventually have faded away much of the need for EJB per se.
Again, the devil is in the details. Remember too though that our pruning process is designed not to leave customers behind as we evolve our technology.

> * JSF:
> JSF managed beans and scopes are a set of endless confusion for Java EE developers. It's best to gradually prune these or simply leave them be and find ways to better merge JSF with CDI. It's also very embarrassing that things like JSF converters and filters don't support injection, etc.

I'll let the JSF spec lead follow up on this one.....

> * JAX-RS:
> JAX-RS doesn't really need a lot of special treatment. You can probably place JAX-RS annotations on managed beans of various flavors. It's probably also OK i most cases for JAX-RS annotated managed beans to be injectable (into other components) as well. Some of this probably applies to JAX-WS as well.

If they are injectable, what should the semantics be? Do they still function as JAX-RS resource classes for incoming HTTP requests? Ditto JAX-WS.

> * Servlet:
> Similar to JAX-RS, Servlet related components probably don't need much special treatment either other than the fact that it makes little sense to make them injectable.

See my comments below regarding the differences between matrix 3 and matrix 4. Why does it not make sense for servlets to be injectable but JAX-RS and JAX-WS endpoints?

> * JPA:
> As I've mentioned in the past, we should seriously consider ways of making JPA entities just another managed bean with full access to things like injection. This is really pretty crucial if Java EE is to fully support DDD. Spring enables this today already and it is a source of competitive advantage.

Could you be more specific here? What would it mean for a JPA entity to be a contextual object? You should feel free to raise the issue of injection into JPA entities in the JPA expert group and/or file an RFE there so that we can track as something to consider in a future release.

> * Bean Validation:
> This is really the right model that other Java EE APIs could try and emulate. It has little in terms of it's own component model/life-cycle but just defines annotation based services/SPIs that can be placed on any candidate managed bean. We should see if bean validation can be even better incorporated to JAX-RS and the like.
> I hope this makes sense and helps. I am happy to explain anything further or try to help formulate concrete proposals.

It does -- we appreciate your sharing your perspectives. It would be helpful if you could also comment specifically on some of the issues raised in my email below as to some of the potential steps that we might consider with regard to specific functionality.

thanks again,


> Mar 29, 2012 05:53:14 PM, jsr342-experts_at_javaee-spec.java.net wrote:
> ===========================================
> One of the issues we're grappling with in this release is better
> alignment between Java EE and CDI in the treatment of managed beans.
> There has been some confusion in the community as to what a Java EE
> Managed Bean is, and how Java EE Managed Beans relate to CDI.
> Java EE 6 introduced the Managed Beans specification in order to
> better define a spectrum of functionality applicable to Java EE
> managed objects. Basic Managed Beans are container-managed objects
> with minimal requirements that support a small set of basic services,
> such as resource injection, lifecycle callbacks, interceptors, and the
> ability to be looked up in JNDI or injected.
> Modifications of the basic Managed Beans model that are allowed and
> explicitly foreseen by the Managed Bean specification include:
> * Other ways to declare Managed Beans
> * Other ways to declare constructors of Managed Beans
> * Other ways to assign a name to a Managed Bean
> * Other lifecycle models
> * The ability to have an own java:comp namespace
> * The ability to specify other threading requirements
> * The ability to have a different interceptor facility
> In defining Managed Beans this way, our intention has been to cover a
> spectrum of common functionalities under which to align our component
> models as they evolve.
> CDI managed beans are also defined very minimally: they are required
> to have a no-arg constructor or a constructor annotated @Inject. (See
> CDI 3.1.1 for a more precise definition).
> CDI managed beans support the following functionality (not intended as
> an exhaustive list): they are contextual objects, having a
> well-defined lifecycle or scope that is managed by CDI; they can have
> other beans and resources be injected into them; they can be injected
> into other managed objects; they can have qualifiers, which support
> type-safe injection; they can have interceptors, decorators, and
> observer methods; they can have producer methods and producer fields,
> which in turn can be sources of other managed beans.
> Because CDI managed beans are defined so minimally--any class that has
> a no-arg constructor can be a CDI managed bean--many of the Java EE
> managed classes, in particular those listed in Table EE.5-1 of the
> Java EE specification ("Component classes supporting injection"), can
> be treated as CDI managed beans. Today, however, only Session Beans
> retain their platform-defined component behaviors when treated as CDI
> managed beans. Thus, for example, while a Servlet class (annotated
> with @WebServlet) can be injected with @Inject into a CDI managed bean
> or into an EJB, the instance that is injected does not have the
> ability to service HTTP requests.
> See the attached file Matrix1, which attempts to characterize the
> managed classes of the Java EE platform with regard to CDI
> functionality in a more graphic way. This is as things stand today.
> Notice that while some CDI functionality that is applicable to CDI
> managed beans (including sessions beans) has been extended beyond
> these types, it is not extended in a uniform way. For example,
> Message Driven Beans support CDI interceptors, although they don't
> support the other CDI functionality that session beans do.
> There is also an alignment issue within the Java EE component types
> themselves (EJBs, Servlets, JAX-RS resource classes, web service
> endpoints). For example, only EJBs currently and ManagedBeans support
> Java EE interceptors. JAX-RS endpoints support interceptors if their
> implementation class is an EJB or a ManagedBean. Web service endpoints
> support interceptors if their implementation class is an EJB.
> We think the current state of affairs needs clarification, and would
> like to find a way to better align the notions of CDI managed bean,
> Java EE Managed Bean, and Component class supporting injection.
> We see several possibilities.
> (1) "Do-nothing option"
> Do nothing except add clarification to the Platform specification that
> only EJB session bean (and, trivially, @ManagedBean) components retain
> their Java EE defined component behaviors when used as CDI managed
> beans.
> (2) "First- and second- class managed objects option"
> Distinguish two distinct groups of what are currently referred to in
> Table EE.5.1. as "component classes": Components and auxiliary
> component classes. As suggested in the earlier discussion in this
> expert group, define the notion of "Component class" (used in Table
> EE.5.1) more narrowly around the current component types: EJB,
> Servlet, Managed Bean, and Java EE managed classes using these as
> implementation types (JAX-RS resource classes and web service
> endpoints). In other words, distinguish two distinct groups of what
> the specification currently characterizes as "component classes":
> component classes proper, and auxiliary component classes (e.g.,
> filters, listeners, interceptors, ...). In addition, align the notion
> of Java EE Managed Beans around container services that such types
> would support (or do already support): such as container-managed
> transactions, container-managed security, async invocation, and
> timers/timerservice. Such services would extend also to CDI managed
> beans, but Java EE components other than Session Beans and Managed
> Beans would not retain their Java EE component behaviors when used as
> CDI managed beans. Note that container-managed transactions,
> container-managed security, and async invocation are candidates for
> support via CDI interceptors. It would be desirable if we could
> support timer service notifications as container-managed events using
> the CDI event/observer functionality.
> Matrix2 illustrates this. The blue background highlights the
> changes from Matrix1. The functional change to the initial matrix is
> that interceptor support would be extended to Servlets and JAX-RS
> resource classes and more uniformly to EJBs and Managed Beans. (While
> I've included timer support in this matrix as well, to illustrate how
> these capabilities could evolve, we have no current plans to enhance
> timer support in Java EE 7.)
> Notice that this also removes the anomaly with regard to the
> treatment of MDBs that I mentioned above. It has the disadvantage,
> however, that CDI features are still not uniformly supported for Java EE components.
> (2a) "Option 2 + prune the Managed Bean spec option"
> Abandon the attempted generalizations of Managed Beans in Section
> MB.2.2 of the Managed Beans specification, and define Java EE
> ManagedBeans in terms of the "Basic Model" only. [This is the same
> matrix as Matrix2.]
> (3) "More CDI functionality extended into Java EE Components option"
> In addition to the changes in (2), attempt to merge the notions of
> Java EE Managed Beans and CDI managed beans so that the other Java EE
> component types support more of the CDI functionality (i.e.,
> interceptors, decorators, observer methods, producer methods/fields),
> while retaining their behavior as Java EE components. An exception
> here might be made for the ability to inject these into other
> components while preserving their Java EE behavior. For example,
> injection into other beans might be restricted to those components
> that support a local view rather than remote invocation via HTTP, web
> services, JMS, RMI, etc.
> Matrix3 illustrates this. The green background highlights the
> changes beyond Matrix2.
> (4) "Injected components behave as components"
> In addition to (3), Java EE components retain their component behavior
> when injected. For example, the Servlet instance that would be
> obtained via injection would be the same Servlet instance that the web
> container was using to service HTTP requests, and similarly for the
> other Java EE component types.
> Matrix4 illustrates this, using the purple background to highlight
> the changes beyond Matrix3.
> (5) "All Java EE component classes become Java EE ManagedBeans option"
> In addition to the changes in (2), extend the notion of Java EE
> ManagedBean to all container managed classes in Table EE.5.1. In
> addition to resource injection (which these classes already support),
> they would also have lifecycle callbacks, interceptors, timer support,
> and the ability to be looked up in JNDI. The functional change is
> that servlet filters, listeners, interceptors, etc. would get these
> features.
> Matrix5 illustrates the change in functionality. The pink
> background highlights the changes beyond Matrix2.
> (6) "Everything is a managed bean option"
> Both first- and second-class managed classes support CDI managed bean
> capabilities.
> Matrix 6 illustrates this. It includes the features of both
> Matrix4 and Matrix5. The yellow background highlights the addition of
> CDI functionality beyond the features of Matrix4 and Matrix5.
> We need your feedback!!
> We realize that this is a lot of information to digest, but we really
> need you to consider it all carefully and to provide your feedback.
> These issues have very considerably impact on how we go forward with
> managed bean support in the Java EE Platform.
> thanks,
> -Linda